The 65-year-old Clinton, who's expected to leave her job soon, was recovering at home after the incident last week and is being monitored by doctors, according to a statement by aide Philippe Reines.
Dr. Lisa Bardack of the Mt. Kisco Medical Group and Dr. Gigi El-Bayoumi of George Washington University said Saturday that Clinton was suffering from a stomach virus and fainted after becoming extremely dehydrated. The doctors said they recommended that Clinton continue to rest and avoid strenuous activity and cancel all work events for the next week.
Clinton was diagnosed with a concussion Thursday after fainting at home earlier this week, according to a State Department official who spoke on the condition of anonymity because he was not authorized to discuss Clinton's injury publicly. The doctors did not determine it to be a "severe" concussion, the official said.
President Barack Obama telephoned his top diplomat Saturday to wish her well, a White House official said.
The State Department said in a statement that Clinton will continue to work from home in the week ahead and looks forward to returning to the office "soon," the statement said.
The Senate Foreign Relations Committee said it won't hear from Clinton as planned at a Thursday hearing into the Sept. 11 attack against a U.S. diplomatic outpost in Benghazi, Libya, that killed four Americans, including the U.S. ambassador. The House Foreign Affairs Committee also said Clinton would no longer give scheduled testimony at its hearing Thursday on Libya.
Senior State Department officials William Burns and Thomas Nides are to take Clinton's place at both hearings.
Clinton's aides on Saturday informed the Senate committee chairman, Sen. John Kerry, about her health, and the Massachusetts Democrat "insisted that given her condition, she could not and should not appear" as planned, said Kerry spokeswoman Jodi Seth. Obama is expected to nominate Kerry to succeed Clinton.
Clinton backed out of a trip to North Africa and the Persian Gulf on Monday because she was sick. She caught the virus during a recent visit to Europe.
The former first lady is known for her grueling travel schedule and is the most traveled secretary of state, having visited 112 countries while in the job.